The present invention relates to determining the relative concentrations of oil and water (i.e., oil-phase and water-phase fluids) within subterranean reservoirs by measuring a chromatographic separation of tracers having distinctly different partitioning coefficients in the oil and water phase fluids in the reservoir. More particularly, the present invention relates to improving a process for making such a determination by injecting an aqueous solution of reactants which are substantially insoluble in oil but react within the reservoir to convert the injected solution to an aqueous solution containing a substantially oil-insoluble water tracer and a gaseous oil tracer which partitions between oil and water phase fluids.
In 1969 a method for determining the relative amounts of oil and water fluid phases within a subterranean reservoir by injecting an aqueous carrier fluid containing a reactant capable of forming within the formation at least two tracers which have different partitioning coefficients between the carrier fluid and the oil (as exemplified by such tracers formed by hydrolyzing ethyl acetate), and measuring a chromatographically-induced separation between the tracers, was described in U.S. Pat. No. 3,623,842. U.S. Pat. No. 3,751,226 by R. J. Hesse and R. F. Farmer relates to improving such a process by injecting a solution in which the tracer forming reactant is a hydrolyzable beta-keto ester such as ethylacetolacetate. U.S. Pat. No. 3,847,548 relates to improving such a process by injecting carrier fluid containing tracers which partition differently with respect to temperature changes and injecting that fluid at a temperature different from the reservoir temperature. U.S. Pat. No. 3,856,468 relates to improving such a process by injecting carrier fluid containing both a precursor which forms a tracer material that partitions between the fluid phases and a tracer material which s inert and substantially completely dissolved in the mobile phase. U.S. Pat. No. 3,990,298 relates to improving such a process by injecting a carrier fluid containing a plurality of precursors each of which forms a tracer which has a distinctive partition coefficient with at least one mobile fluid phase within the reservoir. U.S. Pat. Nos. 4,099,565 and 4,168,746 relate to uses of such a fluid saturation determining process for evaluating the effectiveness of a design process for recovering oil.